1. Field of the Invention
The present invention relates to headphone interfaces, and, more particularly, to infrared headphone interfaces.
2. Description of the Related Art
Typical infrared (IR) headphone transmitters use analog FM modulators that require manual adjustment to calibrate the carrier frequencies. FIG. 1 is a schematic block diagram of an infrared (IR) headphone system of the prior art using analog technology. The audio is transmitted by an FM carrier (Left and Right channels at 2.3 MHz and 2.8 MHz carrier frequencies, respectively). The modulated frequency may be directly proportional to the instantaneous audio. That is, a maximum audio level would yield a maximum frequency. Alternately, the modulated frequency could be inversely proportional to the instantaneous audio. That is, a maximum audio level would yield a minimum frequency. However, in both cases, the audio level is related to the frequency deviation ±the carrier frequency.
Neither anticipated nor obvious in view of the prior art, however, is an IR headphone system using digital technology.